1. Field of the Invention
The present invention relates to a processor for generating a three-dimensional form model of an appropriate amount of data from the original three-dimensional form data.
2. Description of the Prior Art
Active stereo methods are used for measuring a form of an object of various kinds including a human body without contact with the object at a fast speed. A slit projection method, referred to light cutting method generally, is a representative method thereof. In these methods, an object is imaged by illuminating it with a light for detection, and a three-dimensional image (or distance image) is generated by using the principle of trigonometry. A three-dimensional image consists of a set of pixels in correspondence to three-dimensional positions of points of the object. The slit light projection method uses a slit light having a linear section as the light for detection.
A three-dimensional form model of a whole object can be generated by imaging the object from a plurality of positions and by synthesizing three-dimensional images appropriately. The three-dimensional form model or a part thereof of an object can be used for computer graphics, computer-aided design or the like.
The pixel density of a three-dimensional image in the above-mentioned active stereo methods are constant in the image. When an object is imaged, the pixel density is usually set high in order to measure complicated portions in the form of the object correctly. Then, even three-dimensional positions of portions having relatively simple forms are read at the same pixel density. Therefore, the number of pixels in the whole picture is large, and an amount of the data on the three-dimensional form of the object becomes excessive. If only a portion of the object is important, the measured data includes data for portions not so important, and the amount of the data for the portions not so important becomes excessive unnecessarily. If the amount of the data is excessive, data processing takes an unnecessary long time for computer graphics or the like, and display speed becomes low.
Various techniques have been proposed to reduce the amount of data of three-dimensional form model using polygon representation. For example, it is proposed to delete a vertex from the data in the order of shortness of the distance of vertices from an average polygon of adjacent polygons until the thinning ratio increases to a specified value (xe2x80x9cDicimation of Triangle Meshesxe2x80x9d, Computer Graphics, Vol. 26, No. 2, July 1992). It is also proposed to assign triangular meshes to a continuous portion of the same color on the object (xe2x80x9cAdaptive Sampling and Reconstruction for Discontinuity Preserving Texture-Mapped Triangulationxe2x80x9d, Proceedings of IEEE 2nd CAD-Based Vision Workshop, Feb. 8-10, 1994).
However, in the previous techniques, the amount of the three-dimensional form data are reduced irrespective of boundaries of color textures of the object. Therefore, the form data after reduction has limited applications. For example, if a pattern exists on a flat plane of the object, the pattern cannot be extracted as a form component.
An object of the present invention is to reduce the amount of three-dimensional form data without deleting information on the color boundaries of an object.
In one aspect of the invention, a processor for three-dimensional data of an object receives three-dimensional coordinate data of points of an object, and color image data in correspondence to the coordinate data. Then, color image data are detected at boundaries between first color and second colors different from each other, and the coordinate data are thinned out except the coordinate data in correspondence to the data at the detected boundaries.
An advantage of the present invention is that the amount of three-dimensional form data can be reduced to an appropriate amount of data including useful information, without losing information on color boundaries of the object.